Metal pickling



252. COMPOSITIONS,

Paenea" Jul 31 1928.

UNITED STATES 5am. {ref -5 JAMES H. GRAVELL AND ALFRED DOUTY, 0F ELKINS YARK, PENNSYLVANIA; SAID IDO'UTY ASSIGNOR T0 SAID GRAVELL.

METAL PICKLING.

NoDrawing.

This invention relates generally to acid baths for cleaning metal and particularly to the art of pickling iron and steel.

The objects of the invention are to selectively cont-r01 the action of the pickling bath so as to restrain the action of the bath on the true metalwithquthiii defiiig its scale removiig lpioiierties; to selectively control the bath without marring the appearance of the work, without slowing up the pickling operation and without producing harmful fumes; to mitigate the evils of acid brittleness, blisters, black deposits, pitting and overpickling; to produce cleaner and smoother pickled metal; to enable the pickling operation to be carried out at greater speed; to increase the range of pickling temperatures, and to generally improve the art of pickling metal. It is a further object of this invention to provide a new composition of matter which simultaneously acts as a selective control material and as a material for preventing the pollution of the atmosphere with harmful-fumes; to provide such a material in convenient form and one that can be handled without risk or danger, and one that may be stored for indefinite periods without change in its composition or loss of its desirable properties.

It is common practice to pickle iron and steel in a heated bath consisting of:

Water 95.000 gallons Sulphuric acid (66 B.) 5.000 gallons This bat-h although acting quickly to remove the scale, is not entirely satisfactory due to its violent action on the good metal. This results in much waste of good metal and good acid and the generation of a large volume of hydrogen which pollutes the atmosphere with entrained acid fumes and also causes acid brittleness and blisters.

In order to mitigate these disadvantages various adjuncts may be added to the bat-h for specific purposes. One class of adjuncts may be used to.cr eate afoam over the bath to entrap the escapihg hydrogen long enough to enable it to deposit its moisture so that when it finally escapes it does not pollute the surrounding air. Another class may be used for selectively controlling the action of the bath so that after the scale has been removed the actionon the good metal is reduced thus diminishing the Waste of metal and acid and the generation of hydrogen.

Application filed November 12, 1926. Serial No. 148,093.

Still another class of adjuncts may be used to cause the scale, which normally is removed by flaking off from the surface due to the destruction of the bond between it and the metal itself by the action of the bath, to actually dissolve, thus speeding up the action of the bath so that the good metal is exposed for a shorter time and the waste of acid and metal that would otherwise follow is avoided.

The adjuncts used for selectively control.

ling the pickling baths may be divided into two classes, organic and inorganic.

Among the organic controls are found anthracene residues,oil sliidge'tar, gelatine, gluclpiiigoitnlcohols;yellowon from the manu acture of butyl alcohol, resins' and formaldehyde. 'lhei'norganic controls are confined mostly tOJLIjSgIllC or.o.to ometalswwhich plate out on the metal beingmickled and thus tend to protect it. v

Both classes of control adjuncts are effec tive in the proportion in which they are used but in addition to acting as selective controls, they have certain objectionable effects such as slowing up the pickling operation, producing obnoxious vapors, coating the work with objectionable deposits and otherwise tending to do harm and thus it is that the cont-r01 effect obtainable is limited by the tolerance of the evil effects.

When the scale dissolving adjuncts are employed, much more acid is consumed than in those methods where the scale is simply stripped from the metal and falls to the bottom of the bath where it remains undissolved.

We have discovered that stannoustin, or tin appearing as a bivalentfa tom as distinguished from tin appearing in compounds as a quadrivalent atom, acts as a powerful selective control adjunct and has an advantage over all other controls known to us in that it does not mai-teriallwliag o era' pro uce harm ul umes or es'i iiid g e j bat or otherwise injg r e the pi g kled work. However, the amount that can be tolerated in a pickling bath is limited by its peculiar effect of causing the otherwise insoluble scale to be acted on by the acid bath, thus enabling it to enter into solution, thus tending to quickly exhaust the acid. From a commercial standpoint there is also another governing factor prohibiting the use of relatively large amounts of stannous tin; the most economical source of stannous tin at. -v w is stannous chloride (SnCl 2I-I O), a cheap and easily obtainable commercial salt, but this generates so much hydrochloric acid in the bath that is used for pickling iron and steel that copper is dissolved from the bronze fittings used in the pickling bath for supporting work, introducing steam, etc., and deposited in the form of a plate on the work being pickled, thus producing an objectionable finish.

We have further discovered, however, that the disadvantageous results which constituted limitations in the use of stannous salts, including stannous chloride, in a sulphuric acid bath may be overcome and the same degree of selective control obtained as if large amounts of stannous tin were present, by using simultaneously relatively small amounts of both stannous tiwrganlnzan plrganlic selective control a 'unct. e t at t e two type fcfififibrd o not act independ- ,ently producing merely an additive effect, but that the actual control produced is greatly in excess of this. We have noted this augmented effect with such combinations as stannous tin with glue, gelatine, formaldehyde, nitrogen ring compounds, bran liquor, flour, anthracene residues, and oil sludge tar.

On investigating further we find that admixture of arsenic with various organic selective control adjuncts result in control effects greater than the additive effects of the materials of the admixture, and we have concluded that generally considered the use control effects.

We find further that sulphite pulp waste liquor, a by-product of wood pulp manufacture, although having but a mild selective control effect when used alone, particularly magnifies the effect of stannous tin. In addition to affording one of the best combinations with stannous tin for securing selective control, it has the property of producing a blanket of foam on the bath which, not only prevents the pollution of the atmosphere by keeping the escaping hydrogen in long enough for it to deposit its moisture, but also serves to keep the air out of the bath, thus prolonging the life of the stannous salt by preventing its precipitation as a basic salt, which would render it ineffective as a selective control adjunct.

We have found that other materials besides sulphite pulp waste liquor have this property of forming a blanket of foam that protects the tin against the action of the air, among which are saponin, licorice, flour, rye meal and sumac leaves, and our experiments indicate that these foam producing materials possess mild selective control properties from which we have concluded that it is a general property of foam producing material to exert more or less selective control properties.

We have found that a suitable proportion of stannous chloride that may be used in a sulphuric acid pickling bath for iron and steel without danger of dissolving the scale or Causing a deposit of copper on the work 1s:

Water 95.000 gallons Sulphuric acid 5.000 gallons Stannous chloride .015 pounds Experiments indicate that this amount of stannous tin reduces the baths attack on iron and steel to about 75%.

Similar experiments indicate that to reduce the baths attack the same amountby the use of sulphite pulp waste liquor (which contains about 50% solid matter) alone would require .270 pounds.

It would be natural to expect that when the two adjuncts are used simultaneously in thelamounts as shown in the following formu a:

VVa-ter 95.000 gallons Sulphuric acid (66) 5.000 gallons Stannous chloride .015 pounds (SnCl 2H O) Sulphite pulp waste liquor (as described) .270 pounds that the control effect would be the product of the two effects considered separately, thus resulting in a reduction of the baths attack to 56%. However that may be, our experiments indicate that the baths attack on the metal is really much less, being only 13%, thus specifically illustrating the combined effect of stannous tin and an organic selective control adjunct.

Although the two adjuncts may be added separately to the bath we find it more convenient to evaporate the sulphite pulp waste liquor to dryness and after reducing it to a powder, admix pulverized stannous chloride with it. As about one half of the waste liquor is solids, after evaporation, one half of the original weight suffices for our purpose, thus the following admixture produces suificient adjunct for our pickling bath of 100 gallons.

Stannous chloride 015 pounds (SnCl 2I-I O) Evaporated sulphite p ulp waste liquor 135 pounds 252. COMPOSITIONS,

sulphate satisfactory when used in the following proportions:

Stannous chloride .015 pounds (SnCl QH O) Evaporated sulphite p ulp waste liquor 135 pounds Anhydrous sodium sulphate 350 pounds This produces a composition that remains stable in the atmosphere and one that may be handled without risk or danger. The proportions indicated produce sufficient for selectively controlling a bath of 100 gallons although more or less may be used to suit individual needs, as its effect Varies with the amount employed.

To carry out the pickling process with our adjunct we prepare the sulphuric acid bath in the regular way by adding suflicient acid to a water bath, which may or may not be heated, after which We add our adjunct in sufficient amounts to secure the desired control. We then immerse the Work to be pickled. The acid attacks the metal where it is in contact with the scale and in so doing generates gaseous hydrogen which acts to blow off the scale. The scale settles to the bottom of the bath and remains undissolved. As soon as the scale leaves the surface of the metal the action of the acid on the metal is checked and the generation of hydrogen is correspondingly diminished. Thus it-is that the available hydrogen necessary for the production of acid brittleness is so reduced that the work is not seriously affected. What hydrogen does escape is entraped in anautomatically formed blanket of foam, for sutficient time for it to deposit its moisture, so that when it finally does escape, it carries no acid mist with it and hence does not pollute the atmosphere. The work may be left in the bath till all obstinate patches of scale are removed, because the bath has so little eflect on the cleaned metal that there is no danger of spoiling the work by overpickling.

By adding a relatively large amount of our selective control adjunct, the acid strength of the bath may be materially augmented without danger of over-pickling the Work or marring its appearance, thus enabling the pickling operation to be carried out at greater speed or the pickling temperature may be greatly reduced without reducing the speed of pickling.

After the work has been removed from the bath we have noted that blistering and acid brittleness is less than when the work is pickled in the usual way, and it is so clean, smooth and bright that it can be readily distinguished from work pickled by baths used prior to our invention. We attribute this general improvement in the pickled work to our ability to secure a high degree of selective control without the use of excessive amounts of adjunct material.

If desired, the work after pickling may be washed in water to remove an excess of the pickling liquor and then dipped into lime water or other material to neutralize or remove all traces of acidity and thus prevent or retard the formation of rust.

Although our invention is directed specifically to the pickling of iron and steel in a sulphuric acid bath it should be understood that the invention may be applied to the ickling of ther metals such as co er m and that other acidsuch as iloric and hosphoric may be used ins ead of sulphuric aci and as the invention is of a chemical nature, we desire to avail ourselves of the doctrine of equivalents.-

lVe claim:

1. An acid pickling bath for metal containing stannous tin in limited quantity substantially as described suflicient to selectively control the bath and insufiicientto cause the bath to dissolve scale.

2. An acid pickling bath for iron and steel containing stannous tin in limited quantity substantially as described sufiicient to selectively control the bath and insuflicient to cause the bath to dissolve scale.

3. A sulphuric acid pickling bath for iron and steel containing stannous tin in limited quantity substantially as described suflicient to selectively control the bath and insufficient to cause the bath to dissolve the scale.

4. A sulphuric acid pickling bath for iron and steel containing stannous chloride in limited quantity substantially as described sufficient to selectively control the bath but insuflicient to cause the bath to dissolve scale.

5. An acid bath for pickling metal containing both stannous tin in limited quantity insuflicient to cause the bath to dissolve scale and sufiicient to selectively control the bath and sulphite pulp waste liquor.

6. A sulphuric acid pickling bath for iron and steel containing both stannous tin in limited quantity insuflicient to cause the bath to dissolve scale and sufiicient to selectively control the bath and sulphite pulp waste liquor.

7. An acid pickling bath for metal containing both stannous tin in quantity sufficient to selectively control the said bath and insufficient to cause the bath to dissolve the scale of said metal, and an organic selective control material.

8. An acid pickling bath for metal containing both stannous tin in amount suflicient to selectively control the said bath but insufficientto cause the bath to dissolve the scale of said metal, and an organic selective control material adapted to produce a blanket of foam on said bath.

9. A sulphuric acid pickling bath for iron and steel containing both stannous chloride ic fiiiii in amount suflicient to selectively control the said bath and insufficient to cause the bath to dissolve the scale of said metal, and an organic selective control material capable of producing a blanket of foam on said bath.

10. A sulphuric acid pickling bath for iron and steel containing both stannous chloride in amount sufficient to selectively control the said bath and insufiicient to cause the said bath to dissolve the scale of said metal and sulphite pulp waste liquor.

11. A composition of matter for selectively controlling an acid pickling bath for metal containing an admixture of stannous tin in limited quantity insufficient to cause the bath to dissolve scale and sufficient to selectively control the bath and an organic selective control material. 

